Life History and Population Energetics of the Dobson Fly, Corydalus Cornutus

Abstract

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Production of Dobsonfly (Corydalus cornutus) Larvae in the New River of West Virginia

“…The annual production of C. comutus larvae in the New River (3.1 g m" was less than production of larvae in four Texas streams (Brown andFitzpatrick 1978, Short et al 1987), although the substantial variance of the density estimates used to calculate production of New River larvae precluded valid comparisons with production estimates derived from other populations. Two causes for potentially true differences between estimated annual production of New River larvae and that in the Texas streams relate to ineffective sampling of age-0 larvae from the New River and a shorter growing season there.…”

“…Coydalus comutus occurs throughout North America east of the continental divide (Chandler 1956, Merritt andCummins 1984), but the few detailed studies are of southern (Georgia and Texas), univoltine populations (Brown and Fitzpatrick 1978, Benke et al 1984, Short et al 1987. C. comutus in more northern regions (Michigan) have two-or three-year life cycles (Chandler 1956, Knight andSimmons 1975), and those in the New River have a two-year life cycle, suggesting that growth and voltinism in this species are governed by latitudinal temperature effects.…”

“…New River C. comutus larvae may experience a thermal regime that is near-optimal in this respect, because voltinism is intermediate in comparison to other reported life histories. Brown and Fitzpatrick (1978) studied an univoltine population of C. comutus in Texas, where the average larva hatched in mid-June and emerged from the river to pupate in early June of the next year. Similar life histories were reported by Benke et al (1984) in Georgia and Short et al (1987) in Texas.…”

“…Two causes for potentially true differences between estimated annual production of New River larvae and that in the Texas streams relate to ineffective sampling of age-0 larvae from the New River and a shorter growing season there. Early-instar larvae contribute substantially to the total production of a C. comutus population (Brown and Fitzpatrick 1978). Short et al (1987) attributed the variation in larval production in the Texas streams to differences in thermal regimes (that is, length of growing season); production in those streams varied from 9.72 to 79.14 g m-2…”

“…Age-0 larvae were not fully recruited to the capture gear, precluding reasonable estimates of their production. We assumed that all production occurred when water temperatures equaled or exceeded 10 "C (Brown and Fitzpatrick 1978), which was 22 March to 22 November. Production was calculated by the instantaneous growth method (Ricker 1975), where, for a given time interval, production was the multiple of mean biomass and instantaneous growth in weight.…”